Stall flutter mitigation of an airfoil by active surface morphing

Stall flutter is a large-amplitude, flow-induced limit cycle oscillation that poses a risk of structural failure of wings. In this paper, a numerical investigation is conducted to explore the mitigation of stall flutter using active surface morphing with a single-mode harmonic motion at a Reynolds number of 1000. The effects of oscillation position and phase on mitigation are evaluated based on the net energy gain of the airfoil over one oscillation cycle. The results show the effectiveness of active surface morphing in mitigating stall flutter, achieving a maximum of 46% reduction in energy obtained by the airfoil from the flow. The control effect is primarily attributed to the decrease in the aerodynamic moment peak during the pitch-up phase and the increase in the aerodynamic moment trough during the pitch-down phase. The former is essentially due to the large-scale clockwise vortex induced by the skin bulging in the pitch-up phase. The latter is fundamentally caused by the weakening of the trailing-edge vortex and the strengthening of the second leading-edge vortex. Finally, maps depicting the energy exchange between the flow and the airfoil system are presented to further demonstrate the control effectiveness of active surface morphing.